"ADSL" is the abbreviation for "asymmetrical digital subscriber line," a technology that is used for transmitting data at high bandwidths. This technology is termed "asymmetric" because the transfer rate to the user, known as the downstream, is far greater than the transfer rate from the user, the upstream.
ADSL uses existing telephone lines and provides connections that are constantly available. A splitter is used to transform a single telephone line into usage for ADSL service and voice calls. Because data and voice can be transferred at the same time, voice calls can be answered while remaining online. According to Search Networking, ADSL data is usually offered at speeds ranging from 512 Kbps to 6 Mbps.